Install green bridges as road crossing structures for bats
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Green bridges are bridges over roads that are covered in vegetation and usually planted with hedgerows and trees. They have been built as mitigation measures usually to guide larger mammals, such as deer, safely across wide roads. A study in Germany found 10 bat species using eight green bridges to fly over a road and also to forage (Bach & Müller-Stiess 2005). However, the study has not been summarised here as it did not provide data that can be used to assess effectiveness, such as a control, or the proportion of bats not using the green bridges. The study described below reports the proportion of bats that are either using a green bridge to cross the road safely or are crossing the road below at risk of collisions with traffic.
Bach L. & Müller-Stiess H. (2005) Fachbeitrag Fledermäuse an ausgewählten Grünbrücken. Effizienzkontrolle von Wildtierpassagen in Baden-Württemberg (FE 02.220/2002/LR) In: Georgii B., Peters-Ostenberg E., Henneberg M., Herman M., Müller-Stiess H. & Bach L. (2007) Nutzung von Grünbrücken und anderen Querungsbauwerken durch Säugetiere. Gesamtbericht zum Forschungs- und Entwicklungsvorhaben 02.247/2002LR.
Supporting evidence from individual studies
A study in 2014 at one green bridge over a road in the UK (Berthinussen & Altringham 2015) found that the green bridge was used by 97% of bats that crossed the road. A greater number of bats crossed the road using the green bridge (97%, 121 of 125 bats) than crossed the road below at traffic height (2.4%, 3 of 125 bats) or above traffic height (0.8%, 1 of 125 bats). Four bat species were recorded using the green bridge for crossing and foraging: common pipistrelle Pipistrellus pipistrellus (92 bats), soprano pipistrelle Pipistrellus pygmaeus (22 bats), Natterer’s bats Myotis nattereri (2 bats), and a whiskered or Brandt’s bat Myotis mystacinus or Myotis brandtii (1 bat). Four bats using the green bridge could not be identified to species. One common pipistrelle and two unidentified bats were recorded crossing the road below the green bridge at traffic height. One common pipistrelle crossed the road below above traffic height. The green bridge was built over a four-lane road in 2005 to maintain access to a historic property and provide a wildlife crossing. The bridge (50 m long x 30 m wide x 6–8 m high) had a paved road over it with grass verges, shrubs and trees (2–3 m high) on each side. Observations of crossing bats and recordings of bat calls were made during 10 x 60 minute surveys at dusk or dawn in June–August 2014.Study and other actions tested